U.S. patent number 7,352,155 [Application Number 11/451,124] was granted by the patent office on 2008-04-01 for apparatus and method for detecting battery pack voltage.
This patent grant is currently assigned to O2Micro International Ltd.. Invention is credited to Guoxing Li, Wei Wang.
United States Patent |
7,352,155 |
Li , et al. |
April 1, 2008 |
Apparatus and method for detecting battery pack voltage
Abstract
An apparatus and method for detecting battery pack voltage is
disclosed. The voltage detection apparatus includes a plurality of
selectors for providing a cell voltage of a predetermined cell, a
detector buffer for receiving the cell voltage of the predetermined
cell and supplying an intermediate voltage, a data process circuit
for processing the intermediate voltage to acquire a voltage value
indicative of the cell voltage of the predetermined cell, wherein
each selector includes a plurality of switches and a plurality of
level shifters, each switch being controlled by one of the
plurality of level shifters to operate with a safe gate-source
voltage, source-bulk voltage and reverse-biased body diode.
Inventors: |
Li; Guoxing (Sunnyvale, CA),
Wang; Wei (Shanghai, CN) |
Assignee: |
O2Micro International Ltd.
(KY)
|
Family
ID: |
38821219 |
Appl.
No.: |
11/451,124 |
Filed: |
June 12, 2006 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20070285054 A1 |
Dec 13, 2007 |
|
Current U.S.
Class: |
320/118; 320/122;
320/120; 320/136; 320/134; 320/132; 320/116 |
Current CPC
Class: |
G01R
31/396 (20190101); B60L 58/22 (20190201); G01R
31/3835 (20190101); Y02T 10/7061 (20130101); Y02T
10/7005 (20130101); Y02T 10/70 (20130101); B60L
2240/547 (20130101); B60L 2250/16 (20130101) |
Current International
Class: |
H02J
7/00 (20060101) |
Field of
Search: |
;320/116,132,118,120,122,134,136 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sterrett; Jeffrey
Assistant Examiner: Hansen; Stuart
Attorney, Agent or Firm: Wang; Li K. Wang Law Firm, Inc.
Claims
What is claimed is:
1. A voltage detection apparatus for a battery pack, the battery
pack having a plurality of battery blocks, each battery block
including a plurality of cells connected in series, each cell
having a positive electrode and a negative electrode, the voltage
detection apparatus comprising: a plurality of selectors, each
selector being coupled to one of the plurality of battery blocks
for determining a predetermined cell, each selector including a
switch box and a switch controller, the switch controller being
capable of receiving at least one voltage signal from the coupled
battery block and controlling a status of the switch box; a
detector buffer coupled to the plurality of selectors for receiving
a cell voltage of the predetermined cell and supplying an
intermediate voltage, the detector buffer having an inverting
terminal and a non-inverting terminal; and a data process circuit
coupled to the detector buffer for processing the intermediate
voltage to acquire a voltage value indicative of the cell voltage
of the predetermined cell.
2. The voltage detection apparatus of claim 1, wherein the switch
box having a plurality of switches, each odd-numbered switch being
coupled to the positive electrode of one of the plurality of cells
in the coupled battery block, and each even-numbered switch being
coupled to the negative electrode of one of the plurality of cells
in the coupled battery block, and wherein the switch controller
having a plurality of level shifters, each level shifter receiving
the at least one voltage signal from the coupled battery block, and
each level shifter being coupled to one of the plurality of
switches for supplying a control signal to the coupled switch.
3. The voltage detection apparatus of claim 2, wherein the
predetermined cell being selected when the odd-numbered and
even-numbered switches respectively coupled to the positive and
negative electrodes of the predetermined cell are turned on.
4. The voltage detection apparatus of claim 2, wherein each level
shifter receiving a selection signal and generating the control
signal according to the selection signal to control the coupled
switch.
5. The voltage detection apparatus of claim 2, wherein the control
signal having a magnitude and the magnitude being determined by the
at least one voltage signal.
6. The voltage detection apparatus of claim 2, wherein each level
shifter further comprising a power terminal and a level terminal,
the power terminal being coupled to the positive electrode of a
first cell in the coupled battery block for receiving a first
voltage signal and the level terminal being coupled to the positive
electrode of a second cell in the coupled battery block for
receiving a second voltage signal.
7. The voltage detection apparatus of claim 6, wherein the first
cell having a highest voltage potential in the coupled battery
block.
8. The voltage detection apparatus of claim 2, wherein each switch
further comprising a first terminal, a second terminal and a
control terminal, the first terminal of each odd-numbered switch
being connected to the positive electrode of one of the plurality
of cells, the first terminal of each even-numbered switch being
connected to the negative electrode of one of the plurality of
cells, the second terminal of each odd-numbered switch being
connected to a first node, the second terminal of each
even-numbered switch being connected to a second node, and the
control terminal of each switch receiving the control signal.
9. The voltage detection apparatus of claim 8, wherein a voltage
difference between the first node and the second node being the
cell voltage of the predetermined cell.
10. The voltage detection apparatus of claim 2, wherein one of the
plurality of switches being a P-MOSFET and a bulk of the P-MOSFET
being connected to a highest voltage potential in the coupled
battery block.
11. The voltage detection apparatus of claim 2, wherein the switch
box further supplying a common mode voltage to the detector buffer
for calibrating the voltage value indicative of the cell voltage of
the predetermined cell.
12. The voltage detection apparatus of claim 11, wherein the common
mode voltage being acquired when a voltage at a predetermined
electrode of the predetermined cell being passed to both the
non-inverting terminal and the inverting terminal of the detector
buffer through the switch box.
13. A method for detecting a voltage of each cell in a battery
pack, the battery pack having a plurality of cells connected in
series, comprising the steps of: predetermining a cell to be
detected in response to a selection signal; receiving at least one
voltage signal from the battery pack; generating a plurality of
control signals according to the selection signal and the at least
one voltage signal; selecting the predetermined cell under control
of the plurality of control signals, the predetermined cell having
a cell voltage; acquiring an intermediate voltage based on the cell
voltage of the predetermined cell; and acquiring a voltage value
indicative of the cell voltage of the predetermined cell according
to the intermediate voltage.
14. The method of claim 13, further comprising the step of
converting the intermediate voltage from analog to digital before
acquiring the voltage value indicative of the cell voltage of the
predetermined cell.
15. The method of claim 13, wherein each control signal having a
magnitude determined by the selection signal and the at least one
voltage signal.
16. The method of claim 13, wherein the step of selecting the
predetermined cell further comprising the steps of: supplying the
plurality of control signals to a plurality of switches; and
turning on the switches that are coupled to the predetermined cell
under control of the plurality of control signals.
17. The method of claim 13, further comprising the steps of:
providing a common mode voltage; and calibrating the voltage value
indicative of the cell voltage of the predetermined cell based on
the common mode voltage.
18. The method of claim 17, wherein the step of providing the
common mode voltage further comprising the steps of: applying a
voltage at a predetermined electrode of the predetermined cell to
the inverting terminal and the non-inverting terminal of a detector
buffer.
19. An electronic system, comprising: a battery pack having a
plurality of cells connected in series, the plurality of battery
cells being divided into a plurality of battery blocks; an
electronic equipment attached to and powered up by the battery
pack; a digital device capable of predetermining a cell from the
plurality of cells and providing selection signals; and a voltage
detection apparatus coupled to the digital device for receiving the
selection signals and coupled to the battery pack for selecting the
predetermined cell according to the selection signals and detecting
a voltage of the predetermined cell, the voltage detection
apparatus including a plurality of switch boxes and a plurality of
switch controllers, each switch box being coupled to one of the
plurality of battery blocks, and each switch controller being
coupled to one of the plurality of battery blocks for receiving
voltage signals and to one of the plurality of switch boxes for
supplying control signals.
20. The electronic equipment system of claim 19, wherein the
control signals determining a status of each switch box to select
the predetermined cell.
21. The electronic equipment system of claim 19, wherein magnitudes
of the control signals ensuring each switch box in normal
operation.
22. The electronic equipment system of claim 21, wherein the
voltage signals from the coupled battery block determining the
magnitudes of the control signals.
Description
FIELD OF THE INVENTION
The present invention relates to voltage detection and in
particular to an apparatus and method for detecting the voltage of
a battery pack.
BACKGROUND OF THE INVENTION
A battery pack is usually composed of a plurality of cells
connected in series for supplying electric power to electronic
equipments such as an electronic vehicle, portable computer,
electronic camera or the like. The battery pack is usually equipped
with a voltage detection apparatus that detects the voltage of each
cell for capacity calculation and protection of each cell.
FIG. 1 illustrates a prior art voltage detection apparatus 100 for
a battery pack in which a plurality of cells are connected in
series. The cell voltage detection apparatus 100 is composed of a
first input selector 101, a second input selector 103, a detector
buffer 105, a data process circuit 110, and a voltage source 111.
Generally, an external display unit 113 is connected to the voltage
detection apparatus 100 to receive and display the measured cell
voltage.
To detect the voltage of each cell in the battery pack, for
example, a cell 120, the first input selector 101 selects the
positive electrode of the cell 120 and the second input selector
103 selects the negative electrode of the cell 120. Through the
first input selector 101 and the second input selector 103, the
voltage of the cell 120 is supplied to the detector buffer 105. In
the detector buffer 105, the voltage of the cell 120 is subjected
to a predetermined calculation to provide an intermediate voltage
to the data process circuit 110. The data process circuit 110
processes the intermediate voltage to obtain a voltage value
indicative of the cell voltage of the cell 120. The data process
circuit 110 may include an analog to digital (A/D) converter 107
and an arithmetic unit 109 as shown in FIG.1 or simply includes a
plurality of comparators to determine the voltage value. In FIG.1,
the A/D converter 107 converts the intermediate voltage from analog
to digital and provides a digital value of the intermediate voltage
to the arithmetic unit 109. The arithmetic unit 109 such as a
microprocessor processes the supplied digital value in a
predetermined manner to acquire the voltage value indicative of the
cell voltage of the cell 120. Finally, the display unit 113 can
indicate the voltage value on a display screen such as a LCD
display panel, plasma display panel, cathode-ray tube (CRT), a
fluorescent character display tube or the like.
However, the first and second input selectors 101 and 103 are
usually composed of semiconductor switching elements produced using
conventional high-voltage complementary metal oxide semiconductor
(CMOS) process. Such switching elements impose limitation on
application of the voltage detection apparatus 100. The limitation
is caused by the fact that the more cells connected in series in
the battery pack, the higher break-down voltage required for the
switching elements in the first and second input selectors 101 and
103, while such switching elements have a low break-down voltage.
Hence taking into account of the low break-down voltage of the
switching elements, there has to be a limitation on the cell number
to ensure the proper operation of the switching elements.
Specially, when the switching elements are constructed of MOSFETs,
to ensure the MOSFETs in normal operation, the gate-source voltage
of each MOSFET should be always within the safety range, further,
the source-bulk voltage of each MOSFET should also be always within
the safety range and the body diode of each MOSFET should always be
reverse-biased.
With respect to the switching elements that have a high break-down
voltage, there may not be such limitation as previously stated.
However, the switching elements with the high break-down voltage
have to be produced using a more complicated and expensive CMOS
process. Consequently, the overall cost of the voltage detection
apparatus 100 is increased. Furthermore, compared with the
switching elements with the low break-down voltage, the die size of
the switching elements with the high break-down voltage usually has
to increase a lot to meet the same turn-on resistance requirement,
which also imposes an increased cost to the voltage detection
apparatus 100. Hence, taking into account of the increased cost and
die size, it is not an ideal solution to adopt the switching
elements produced using the more complicated and expensive CMOS
process to overcome the aforementioned drawbacks.
Accuracy is another aspect that should be taken into account when
evaluating a voltage detection apparatus. Typically, inaccuracy is
caused by some elements in the voltage detection apparatus. Fox
example, in the exemplary voltage detection apparatus 100, a common
mode error usually exists in the detector buffer 105 and can
degrade the accuracy of the voltage detection. To enhance the
accuracy, a common way is to add some supplementary elements or
lines, but this will inevitably complicate the circuitry.
It is therefore an object of the present invention to provide a
voltage detection apparatus and method that can be realized using
the switching elements produced using the high-voltage CMOS
process, and at the same time no cost burden is induced and the
accuracy is enhanced without complicating the circuitry. It is to
such a voltage detection apparatus and method that the present
invention is primarily directed.
SUMMARY OF THE INVENTION
In one embodiment, there is provided a voltage detection apparatus
for a battery pack that has a plurality of battery blocks and each
battery block includes a plurality of cells connected in series.
The voltage detection apparatus includes a plurality of selectors,
a detector buffer and a data process unit, each selector being
coupled to one of the plurality of battery blocks for determining a
predetermined cell and receiving a first voltage signal and a
second voltage signal from the coupled battery block, the detector
buffer being coupled to the plurality of selectors for receiving a
cell voltage of the predetermined cell and supplying an
intermediate voltage, and the data process circuit being coupled to
the detector buffer for processing the intermediate voltage to
acquire a voltage value indicative of the cell voltage of the
predetermined cell.
In another embodiment, there is provided a method for detecting a
voltage of each cell in a battery pack that has a plurality of
cells connected in series. The method includes the steps of
generating a plurality of control signals, each control signal
having an adjustable magnitude, selecting a predetermined cell
under control of the plurality of control signals, the
predetermined cell having a cell voltage, acquiring an intermediate
voltage based on the cell voltage of the predetermined cell, and
acquiring a voltage value indicative of the cell voltage of the
predetermined cell according to the intermediate voltage.
In yet another embodiment, there is provided an electronic system.
The electronic system includes a battery pack having a plurality of
cells connected in series, the plurality of battery cells being
divided into a plurality of battery blocks, an electronic equipment
attached to and powered up by the battery pack, a digital device
capable of predetermining a cell from the plurality of cells and
providing selection signals, and a voltage detection apparatus
being coupled to the digital device for receiving the selection
signals and being coupled to the battery pack for selecting the
predetermined cell according to the selection signals and detecting
a voltage of the predetermined cell, the voltage detection
apparatus further including a plurality of switch boxes and a
plurality of switch controllers, each switch box being coupled to
one of the plurality of battery blocks, and each switch controller
being coupled to one of the plurality of battery blocks for
receiving voltage signals and to one of the plurality of switch
boxes for supplying control signals.
BRIEF DESCRIPTION OF THE DRAWINGS
Advantages of the present invention will be apparent from the
following detailed description of exemplary embodiments thereof,
which description should be considered in conjunction with the
accompanying drawings, in which:
FIG. 1 is a prior art voltage detection apparatus;
FIG. 2 is a block diagram of a voltage detection apparatus in
accordance with one embodiment of the present invention;
FIG. 3 is a schematic diagram of one selector in FIG. 2;
FIG. 4 is a schematic diagram of one level shifter of FIG. 3;
FIG. 5 is a flow chart illustrating operation of the cell voltage
detection apparatus of FIG. 2; and
FIG. 6 is an electronic system in accordance with one embodiment of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Reference will now be made in detail to embodiments of the present
invention. While the invention will be described in conjunction
with the embodiments, it will be understood that they are not
intended to limit the invention to these embodiments. On the
contrary, the invention is intended to cover alternatives,
modifications and equivalents, which may be included within the
spirit and scope of the invention as defined by the appended
claims.
FIG. 2 illustrates a voltage detection apparatus 200 according to
one embodiment of the present invention. The voltage detection
apparatus 200 includes a plurality of selectors 210, a detector
buffer 220 and a data process circuit 230 that includes an A/D
converter 217 and an arithmetic unit 219. The voltage detection
apparatus 200 detects the cell voltage of cells 1A-1 to 3A-N that
are coupled in series. Referring to the cell connection in FIG.2,
the cell 1A-1 has a lowest voltage potential, while the cell 3A-N
has a highest voltage potential Vc1.
The cells 1A-1 to 3A-N are divided into a plurality of battery
blocks, for example, three battery blocks 1A, 2A and 3A. Each
battery block is coupled to one of the plurality of selectors. As
shown in FIG. 2, the battery block 1A is coupled to a selector
210-1, the battery block 2A is coupled to a selector 210-2 and the
battery block 3A is coupled to a selector 210-3. Each selector has
similar circuitry and electrical feature, therefore the selector
210-2 as a representative is depicted in details hereinafter.
The selector 210-2 includes a switch box 201, a switch controller
203, a first resistor 205 and a second resistor 207. The switch box
201 is connected to the battery block 2A for selecting a
predetermined cell from cells 2A-1 to 2A-N. The switch controller
203 is connected to the switch box 201 for controlling a status of
the switch box 201, and the switch controller 203 is further
connected to the battery block 2A for receiving voltage signals.
When the predetermined cell is selected, the voltages at the
positive and negative electrodes of the predetermined cell are
respectively passed to lines 204 and 206 through the switch box
201. The voltages are then provided to the detector buffer 220. In
other words, the cell voltage of the predetermined cell is provided
to the detector buffer 220.
The detector buffer 220 includes an operational amplifier 209, a
third resistor 211, a fourth resistor 213 and a reference voltage
215. The voltage on line 204 is provided to the non-inverting
terminal of the operational amplifier 209 through the first
resistor 205. The voltage on the line 206 is provided to the
inverting terminal of the operational amplifier 209 through the
second resistor 207. The third resistor 211 is connected between
the inverting terminal and the output terminal of the operational
amplifier 209. The non-inverting terminal is further connected to
the ground through the fourth resistor 213 and the reference
voltage 215, and the juncture node of the fourth resistor 213 and
the reference voltage 215 is designated with a reference number 214
as shown in FIG. 2. The reference voltage 215 is capable of
providing a direct current (DC) voltage Vref, so that the voltage
at the juncture node 214 is steadily tied at Vref.
The detector buffer 220 receives the cell voltage of the
predetermined cell and outputs an intermediate voltage at the
output terminal. Assuming the resistances of the first and second
resistors 205 and 207 are equal, and the resistances of the third
and fourth resistors 211 and 213 are equal, the intermediate
voltage can be theoretically calculated according to equation
(1)
##EQU00001## where, Vcell is defined as the cell voltage of the
predetermined cell, Vout is defined as the intermediate voltage, Rc
is defined as the resistance of the third resistor 211 or the
fourth resistor 213, and Ra is defined as the resistance of the
first resistor 205 or the second resistor 207. Assuming the ratio
between Ra and Rc is 2, then the intermediate voltage Vout can be
calculated according to equation (2)
##EQU00002##
Then the intermediate voltage Vout is provided to the A/D converter
217. Meanwhile, the DC reference voltage Vref is also provided to
the A/D converter 217. The intermediate voltage Vout and the DC
reference voltage Vref form a pair of difference inputs V(Vout,
Vref) and are respectively received by the non-inverting terminal
and inverting terminal of the A/D converter 217. The A/D converter
217 converts the intermediate voltage Vout from analog to digital
and provides the digital value of the intermediate voltage to the
arithmetic unit 219. The DC reference voltage Vref is employed for
calibrating the A/D converter 217. The arithmetic unit 219 then
processes the digital value in a predetermined manner to acquire a
voltage value indicative of the voltage of the predetermined
cell.
FIG. 3 illustrates a schematic diagram of the selector 210-2 in
FIG. 2 according to one embodiment. As shown in FIG. 3, the switch
box 201 includes a plurality of switches and the switch controller
203 includes a plurality of level shifters. Each cell from cell
2A-1 to cell 2A-N in the battery block 2A is allocated two switches
respectively connected to the positive and negative electrodes of
the cell. Each switch has a first terminal, a second terminal and a
control terminal. The first terminal of each odd-numbered switch is
connected to the positive electrode of the connected cell, wherein
the odd-numbered switches are respectively designated with
reference symbols 1P to NP. The first terminal of each
even-numbered switch is connected to the negative electrode of the
connected cell, wherein the even-numbered switches are respectively
designated with reference symbols 1N to NN. The second terminal of
each odd-numbered switch is connected together to the first
resistor 205 through line 204. The second terminal of each
even-numbered switch is connected together to the second resistor
207 through line 206. The control terminal of each switch is
connected to one of the level shifters for receiving a control
signal and a status of each switch is determined by the received
control signal.
Further, if a switch in the switch box 201 is constructed of a
P-channel MOSFET (PMOS), to ensure that the source-bulk voltage of
the PMOS switch is within the safety range and the PMOS body diode
is always reverse-biased, the bulk of the PMOS switch should be
connected to the local highest voltage potential Vc2 herein. If a
switch in the switch box is constructed of an N-channel MOSFET
(NMOS), usually, the bulk of the NMOS switch should be connected to
the global ground. For the selector 210-1 in FIG. 2, the local
highest voltage potential is Vc3, and for the selector 210-3 in
FIG. 2, the local highest voltage potential is Vc1.
FIG. 4 illustrates an exemplary schematic diagram of a level
shifter 300-MP in FIG. 3. The exemplary level shifter 300-MP
includes a control unit 310 and a signal generator 320. Powered by
a power source VDD, the control unit 310 receives a selection
signal from a digital device (not shown in FIG.4) at a selection
terminal 303. The selection signal is typically a digital signal,
either value 0 representative of a low voltage level or value 1
representative of a high voltage level. When the selection terminal
303 is provided the value 1, the voltage on line 302 will be set
high while the voltage on line 304 will be set low. Similarly, when
the selection terminal 303 is provided the value 0, the voltage on
line 302 will be set low while the voltage on line 304 will be set
high. In FIG. 4, the control unit 310 is realized by a first
inverter element and a second inverter element. The first inverter
element is connected between the selection terminal 303 and line
304, and formed by metal oxide semiconductor field effect
transistors (MOSFETs) MP1 and MN1. The second inverter element is
connected between line 304 and line 302 and formed by the MOSFETs
MP2 and MN2. However, it should be understood by the skilled in the
art that the control unit can be realized by other conventional
circuitries, and the control unit 310 shown in FIG. 3 is for the
purpose of illustration and not of limitation.
The signal generator 320 includes a first current mirror formed by
MOSFETs MP1A and MP1B, a second current mirror formed by MOSFETs
MP2A and MP2B, a third current mirror formed by MOSFETs MN2A and
MN2B, a first switch MNS1, a second switch MNS2, a first current
source MN1A and a second current source MN1B. Generally, the
switches and current sources are constructed of MOSFETs as shown in
FIG. 4, but it should be understood that the MOSFET structure can
be replaced by other circuitries as long as the necessitated
functionality is realized.
The gate terminal of the first switch MNS1 receives the voltage on
line 302 and the gate terminal of the second switch MNS2 receives
the voltage on line 304. The source terminal of the first switch
MNS1 is connected to the first current source MN1A and the drain
terminal of the first switch MNS1 is connected to the first current
mirror. The source terminal of the second switch MNS2 is connected
to the second current source MN1B and the drain terminal of the
second switch MNS2 is connected to the second current mirror.
The first and second current mirrors are connected to the battery
block 2A shown in FIG. 3 at a power terminal 305. At the power
terminal 305, a first voltage signal from the battery block 2A is
received. The first voltage signal supplies electrical power to the
level shifter 300-MP. For all the level shifters in the selector
210-2, the power terminal is connected to the positive electrode of
the cell 2A-N that has the highest voltage potential Vc2. The first
voltage signal has a voltage level equal to Vc2. The third current
mirror is connected to the first current mirror for copying the
current flowing through the first current mirror. The third current
mirror is also connected to the battery block 2A for receiving a
second voltage signal at a level terminal 307. For the level
shifter 300-MP, supposing the level terminal 307 is connected to
the positive electrode of a test cell that has a voltage potential
a*Vcell1 at the positive electrode, wherein Vcell1 is defined as a
standard voltage of a battery cell, then the second voltage signal
has a voltage level equal to a*Vcell1. The third current mirror is
also connected to the second current mirror at an output terminal
309 through which the control signal is provided to the connected
switch MP in FIG. 3 to determine the status of the connected switch
MP. The magnitude of the control signal is determined by the first
voltage signal and the second voltage signal.
The first and second current sources MN1A and MN1B are further
connected to a current terminal 313 through which a current control
signal is received. The current control signal controls a static
current of the level shifter 300-MP.
When the value 1 is provided to the selection terminal 303, as
previously mentioned, the voltage on line 302 is set to be high
while the voltage on line 304 is set to be low. Consequently, the
first switch MNS1 is turned on and the second switch MNS2 is turned
off. The static current from the first current source MN1A flows
into the MOSFET MP1A through the first switch MNS1. Then copied
sequentially by the first and third current mirrors, the static
current is finally passed to the MOSFET MN2B. Since the MOSFET MN2B
is conductive, the voltage at the output terminal 309 is pushed
down to the voltage at the level terminal 307 that is a*Vcell1. As
shown in FIG. 2, the level shifter 300-MP is connected to the
control terminal of the switch MP that is generally constructed of
MOSFETs. Supposing the switch MP is a PMOS, it can be regarded that
the output terminal 309 is connected to the gate terminal of the
switch MP and the source terminal of the switch MP is connected to
the positive electrode of the cell 2A-M where the voltage potential
is defined as m*Vcell1. So, when the value 1 is provided to the
selection terminal 303, the gate-source voltage of the switch MP is
calculated according to equation (3) Vgs(m)=(a-m)*Vcell1 (3) where
the gate-source voltage of the switch MP is defined as Vgs(m). With
the gate-source voltage computed according to the equation (3), the
switch MP is turned on, and therefore the positive electrode of the
cell 2A-M is selected.
When the value 0 is provided to the selection terminal 303, as
previously mentioned, the voltage on line 302 is set to be low
while the voltage on line 304 is set to be high. Consequently, the
first switch MNS1 is switched off and the second switch MNS2 is
switched on. The static current from the second current source MN1B
flows into the MOSFET MP2A through the second switch MNS2. Then the
static current is copied to the MOSFET MP2B by the second current
mirror. Since the MOSFET MP2B is conductive, the voltage at the
output terminal 309 is pushed up to the voltage at the power
terminal 305 that is equal to Vc2. Similarly, supposing the switch
MP is a PMOS, it can be concluded that when the value 0 is provided
to the selection terminal 303, the gate-source voltage of the
switch MP is calculated according to equation (4)
Vgs(m)=Vc2-m*Vcells (4) With the gate-source voltage computed
according to the equation 4), the switch MP is turned off, and
therefore the positive electrode of the cell 2A-M is isolated.
For the switch MP, it is easy to acquire a gate-source voltage
within the safety range through setting a proper "a*Vcell1" in the
equation 3). In other words, through connecting the level terminal
307 to a proper voltage potential in the battery block 2A, the
gate-source voltage is guaranteed to be within the safety range.
With respect to the equation 4), the gate-source voltage is
steadily within the safety range. Since the gate-source voltage of
the switch MP can be regulated to be always within the safety
range, the low gate-source break-down voltage of the switch
produced with the conventional high-voltage CMOS process will not
impose limitation on applications of the voltage detection
apparatus. Similarly, for other switches in the selectors 210-1,
210-2 and 210-3, equations similar to 3) and 4) can de deduced.
Further, hereinbefore, the equations 3) and 4) are deduced on the
assumption that the switch MP is a PMOS. However, it should be
understood by the skilled in the art that an NMOS can also be
adopted and the equations concerning calculation of the gate-source
voltage can be similarly deduced thereof.
It should be understood that there are other kinds of level shifts
that can realize the same functionality. The disclosed embodiment
of the level shifter herein is for the purpose of illustration and
not of limitation.
FIG. 5 illustrates a flow chart of the cell voltage detection
according to one embodiment of the present invention. It will be
described hereinafter how the voltage detection apparatus 200
detects the cell voltage of the cells 1A-1 to 3A-N.
Firstly, in step 501, a predetermined cell is selected by the
digital device and the voltage of the predetermined cell will be
detected in the following steps. The predetermined cell is supposed
to be the cell 2A-M herein for the purpose of description.
Then, steps 503 and 505 aim to acquire a calibrating voltage for
eliminating the common mode error in the detector buffer 220. As
acknowledged by the skilled in the art, accuracy of the operational
amplifier 209 is impaired by the common mode error and accuracy of
the voltage detection apparatus 200 is consequently degraded. To
enhance the accuracy, it is necessitated to eliminate the common
mode error from the output of the operational amplifier 209.
In step 503, a common mode voltage is selected when the switches MP
and (M+1)N are switched on respectively under control of the level
shifters 300-MP and 300-(M+1)N. Herein the switch (M+1)N is
connected to the negative electrode of the cell 2A-(M+1) which is
neighboring to the cell 2A-M. In this way, the voltage at the
positive electrode of the cell 2A-M is provided to the
non-inverting terminal of the operational amplifier 209
sequentially through the switch MP, line 204 and the first resistor
205. Meanwhile, as shown in FIG. 3, the voltage at the positive
electrode of the cell 2A-M or the negative electrode of the cell
2A-(M+1) is also provided to the inverting terminal of the
operational amplifier 209 sequentially through the switch (M+1)N,
line 206 and the second resistor 207. In other words, the common
mode voltage is provided to the operational amplifier 209 in the
detector buffer 220. Similarly, the common mode voltage can also be
acquired through delivering the voltage at the negative electrode
of the cell 2A-M simultaneously to the non-inverting and inverting
terminals of the operational amplifier 209. Then in step 505, when
the operational amplifier 209 receives the common mode voltage, a
calibrating voltage is outputted at the output terminal of the
operational amplifier 209. The calibrating voltage indicates the
common mode error at the output of the operational amplifier 209.
The calibrating voltage is then received and processed by the data
process unit 230.
After the calibrating voltage is acquired, the voltage detection
apparatus 200 begins to detect the voltage of the predetermined
cell 2A-M. In step 507, the cell voltage of the predetermined cell
2A-M is selected when the switches MP and MN are switched on
respectively under control of the level shifters 300-MP and 300-MN.
In this way, the voltage at the positive electrode of the cell 2A-M
is provided to the non-inverting terminal of the operational
amplifier 209 sequentially through the switch MP, line 204 and the
first resistor 205. Meanwhile, the voltage at the negative
electrode of the cell 2A-M is also provided to the inverting
terminal of the operational amplifier 209 sequentially through the
switch MN, line 206 and the second resistor 207. Then in step 509,
according to the inputs at the non-inverting and inverting
terminals, the operational amplifier 209 outputs an intermediate
voltage at the output terminal. However, as previously stated, the
intermediate voltage includes the common mode error. Step 511 is
for eliminating the common mode error and obtains a voltage value
indicative of the voltage of the predetermined cell 2A-M. After the
intermediate voltage is received and processed by the data process
unit 230, the voltage value is computed through subtracting the
processed calibrating voltage from the processed intermediate
voltage. After obtaining the voltage value, the display unit 113
finally displays the voltage value on the display screen.
The aforementioned voltage detection apparatus can be applied to
various electronic systems. FIG. 6 is an exemplary electronic
system 600 that includes a battery pack 601, an electronic
equipment 603, a voltage detection apparatus 200 and a digital
device 605. The battery pack 601 is composed of a plurality of
cells and is capable of providing an electrical power to the
electronic equipment 603. The electronic equipment 603 can be an
electronic vehicle, portable computer, electronic camera or the
like. The battery pack 601 is further coupled to the voltage
detection apparatus 200 that is capable of detecting the voltage of
each cell in the battery pack 601. The digital device 605 is also
connected to the voltage detection apparatus 200 for determining a
predetermined cell that is to be detected. After the predetermined
cell is determined, the digital device 605 can send selection
signals to the voltage detection apparatus 200 and respond to the
selection signals, the voltage detection apparatus 200 measures the
cell voltage of the predetermined cell. According to the present
invention, since that the gate-source voltage of each switch is
guaranteed to be within the safety range under control of the level
shifter, the switches in the voltage detection apparatus impose no
limitation on application of the voltage detection apparatus.
In operation, the voltage detection apparatus 200 can detect a cell
voltage of the cells 1A-1 to 3A-N used in a portable computer,
electronic camera or the like. To detect the voltage of a
predetermined cell, the cells 1A-1 to 3A-N are firstly divided into
a plurality of battery blocks, for example the battery blocks 1A,
2A and 3A. Each battery block is connected to a selector for
selecting the predetermined cell.
The selector includes a switch box and a switch controller. The
switch controller receives voltage signals from the connected
battery block and selection signals from a digital device. Based on
the voltage signals and selection signals, the switch controller
generates control signals with a predetermined magnitude. Under
control of the control signals, the switch box selects the
predetermined cell. Meanwhile, the predetermined magnitude of the
control signals ensures the switch box in normal operation.
When the predetermined cell is selected, the selector provides the
cell voltage of the predetermined cell to a detector buffer and a
process unit to acquire a voltage value indicative of the cell
voltage of the predetermined cell.
The terms and expressions which have been employed herein are used
as terms of description and not of limitation, and there is no
intention, in the use of such terms and expressions, of excluding
any equivalents of the features shown and described (or portions
thereof), and it is recognized that various modifications are
possible within the scope of the claims. Other modifications,
variations, and alternatives are also possible. Accordingly, the
claims are intended to cover all such equivalents.
* * * * *